1. Field of the Invention
The present invention relates generally to amplifying systems and methods, and more particularly, to amplifying systems and methods which reduce significantly even-order harmonic distortion.
2. Description of the Related Art
Active devices used in amplifiers typically exhibit nonlinearities. As is well-known, such nonlinearities produce unwanted components in the signal at the output of the amplifier. This is particularly the case with amplifiers using semiconductor active devices. Such amplifiers typically produce unwanted D.C. and even and odd order harmonics in the output signal.
Representative of conventional amplifying systems is that shown in U.S. Pat. No. 3,399,356 to Davies. The Davies circuit shows a system employing at least two cascaded tuned emitter stages with an attenuator as a coupling circuit between the stages. The Davies circuit teaches the use of tuned emitter amplifier stages; broad band amplifiers are not taught. The stages are inverting. Further, the relative gains of the amplifiers and the attenuator are not discussed. The Davies system does not address reduction of unwanted harmonic components.
Another patent that is representative of conventional amplifiers is U.S. Pat. No. 3,997,852 to Schornack et al. The Schornack patent shows an r.f. wide band amplifier. An input signal is provided to a transformer, whose output is provided to a field effect transistor attenuator. The output of the field effect transistor attenuator is applied to the input of a field effect transistor amplifier, whose output is provided to a transformer. The output of the amplifier system is provided at the output of this second transformer. The Schornack system only employs one amplifier.
The inventor is also aware of the following additional U.S. patents which are representative of conventional amplifier technology: No. 1,646,438 to Affel; No. 2,440,456 to Ferguson; No. 2,617,039 to Young; No. 2,839,619 to Johnstone; No. 2,840,646 to Bell; No. 3,076,133 to Holcomb; No. 3,246,252 to Beyer; No. 3,633,120 to Battjes; No. 3,729,683 to Hemme; No. 3,863,173 to Scheid et al.; No. 4,074,204 to Broburg et al.; No. 4,155,047 to Rubens et al.; No. 4,301,445 to Robinson; No. 4,367,442 to Tanaka et al.; and No. 4,379,995 to Yamada et al.